linux-kernel - Re: [PATCH v3 02/11] arm64: hugetlb: Refine tlb maintenance scope

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Message-ID: <Z-7zznsJ91ZCCTeS@arm.com>
Date: Thu, 3 Apr 2025 21:47:10 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Will Deacon <will@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Kevin Brodsky <kevin.brodsky@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 02/11] arm64: hugetlb: Refine tlb maintenance scope

On Tue, Mar 04, 2025 at 03:04:32PM +0000, Ryan Roberts wrote:
> When operating on contiguous blocks of ptes (or pmds) for some hugetlb
> sizes, we must honour break-before-make requirements and clear down the
> block to invalid state in the pgtable then invalidate the relevant tlb
> entries before making the pgtable entries valid again.
> 
> However, the tlb maintenance is currently always done assuming the worst
> case stride (PAGE_SIZE), last_level (false) and tlb_level
> (TLBI_TTL_UNKNOWN). We can do much better with the hinting; In reality,
> we know the stride from the huge_pte pgsize, we are always operating
> only on the last level, and we always know the tlb_level, again based on
> pgsize. So let's start providing these hints.
> 
> Additionally, avoid tlb maintenace in set_huge_pte_at().
> Break-before-make is only required if we are transitioning the
> contiguous pte block from valid -> valid. So let's elide the
> clear-and-flush ("break") if the pte range was previously invalid.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>